1. Field of the Invention
The present invention relates to an air cleaner fitting structure for a motorcycle. In particular, the present invention relates to a fitting structure for a connecting tube which connects the air cleaner and a fuel supply system.
2. Description of Background Art
Referring to FIG. 8, for example, as described in Patent Publication No. 2639608, a motorcycle in which a 4-cycle internal combustion engine 04 is suspended from a vehicle frame having a construction such that one mainframe 01 (or a pair of right and left mainframes) extending rearwards from a head pipe is connected to right and left center frames 02. In addition, a carburetor 05 arranged at the rear of the cylinder of the internal combustion engine 04 and an air cleaner 06 arranged at the rear of the center frames 02 are connected by a connecting tube 07.
The air cleaner 06 has a case generally made of resin, which is arranged on the vehicle frame with a rear end of the connecting tube 07 generally made of rubber being fitted thereto in advance. Furthermore, the front end of the connecting tube 07 extending further forward than the air cleaner 06 is fitted by insertion in the mouth of the upstream port of the carburetor 05 already arranged, and fastened by a band, so as to connect the carburetor 05 and the air cleaner 06.
As shown in FIG. 8, since the carburetor 05 at the rear of the cylinder of the internal combustion engine 04 is located slightly ahead of the center frames 02, the band-fastened portion 08 of the front end of the connecting tube 07 and the mouth of the carburetor 05 is located roughly between the center frames 02.
The band-fastened portion is a cross member for supporting the upper end of the rear cushion above the band-fastened portion or for reinforcement, and is located between the center frames 02 at the right and left sides thereof, with little room therebetween.
However, a space for inserting a tool for band-fastening the carburetor 05 and the connecting tube 07 should be ensured for maintenance or the like. As a result, the arrangement and size or shape of the center frames 02 are limited, leaving a limited degree of freedom in securing the rigidity and strength of the frame.
Therefore, a frame line constituted by the mainframe 01 that connects the head pipe and a pivot supporting the rear wheel for swinging movement and the center frame 02 may have a shape making a detour in order to avoid the band-fastening portion. As a result, the weight increases and the center of gravity may move upward.
In view of the above situation, it is an object of the present invention to provide an air cleaner fitting structure for a motorcycle that can form an ideal frame line without being limited in position by the internal combustion engine and the fuel supply system, and can ensure ease of maintenance.
In order to achieve the above object, according to a first aspect of the present invention, an air cleaner fitting structure for a motorcycle having a vehicle frame in which a pair of right and left center frames extend downward, are connected to a mainframe extending rearwards from a head pipe, and have an internal combustion engine arranged in front of the center frame below the main frame is provided. The air cleaner fitting structure includes a connecting tube for connecting an air cleaner arranged further rearwards than the center frame and a fuel supply system at the front thereof is divided into front and rear halves. Furthermore, the division line thereof is at a position further rearwards than the center frame of the vehicle frame.
Since the connecting tube is divided into front and rear halves, even if the arrangement of the internal combustion engine and the fuel supply system such as the carburetor is slightly changed, the division line of the connecting tube can be located at the rear of the center frame. As a result, an operation for connecting or disconnecting the divided front and rear halves of the connecting tube with a band or the like can be easily performed without being hindered by the center frame or the like, thereby improving ease of maintenance.
Specifically, an ideal frame line can be formed without being limited by the position of the internal combustion engine and the fuel supply system such as carburetor or the like, sufficient vehicle frame strength can be ensured, increase in weight and the center of gravity can be avoided, and ease of maintenance can be ensured.
According to a second aspect of the present invention, an air cleaner fitting structure for a motorcycle according to the first aspect is provided, wherein the front half of the divided connecting tube is constructed by a flexible member, and the rear half thereof is constructed by a member having higher rigidity than the front half.
By dividing the connecting tube in two, the front half of the connecting tube is constructed of a flexible member, and the rear half thereof is constructed freely in combination with a member having a higher rigidity than the front half and a member having a low center of gravity. As a result, the connecting tube can be made light, while adequate rigidity is ensured for the connecting tube.
According to a third aspect of the present invention, an air cleaner fitting structure for a motorcycle according to the second aspect is provided, wherein the front half of the connecting tube is made of rubber, and the rear half of the connecting tube is made of resin.
Since the front half of the connecting tube is made of rubber, and the rear half of the connecting tube is made of resin, the connecting tube can be made light, while adequate rigidity for the connecting tube is ensured.
According to a fourth aspect of the present invention, an air cleaner fitting structure for a motorcycle according to the first aspect is provided, wherein a rear cushion is arranged, oriented substantially in the vertical direction, between the air cleaner and the fuel supply system, and the connecting tube is arranged in a prescribed location, avoiding the rear cushion.
Even if the rear cushion is between the air cleaner and the fuel supply system, the division line of the connecting tube is located at the rear of the center frame, so that the front and the rear halves thereof can be connected without being hindered by the rear cushion.
According to a fifth aspect of the present invention, an air cleaner fitting structure for a motorcycle according to the first aspect is provided, wherein the mainframe is a pair of right and left frames having an oblong cylindrical shape in section, and the center frame respectively connected to each mainframe is broad towards the front and rear.
A frame line connecting the head pipe and a pivot supporting the rear wheel for swinging movement is constituted by the mainframe and the center frame, and the frame line constituted by the mainframe and the center frame can be made in an ideal shape without being limited by the position of the internal combustion engine and the fuel supply system, to thereby obtain a strong structure.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.